but the point is, do cyclists receive head injuries any more than anyone else and to what extent are those injuries "severe"?

Anecdotal stories are something everyone can relate to, bit they aren't very accurate for getting a handle of what kind of a problem there really is.

I have a brother who was knocked out by a line drive in baseball, another by a hit in hockey, and uncle who was put out by a golf ball when playing a round. A freind who fell and was hospitalized with a head injury after a fall from a ladder and another friend who died after a fall down a flight of stairs. I've been riding 40 years and have never hit my head, but that doesn't mean someone else hasn't.

Just how big is the problem in relation to everyone else, and just how effective are helmets in preventing "serious" head injuries (and by serious, I'm referring to brain injury)